Field of the Invention
The invention relates to a printed circuit board comprising a plurality of insulating layers and conductive layers, and comprising at least one cavity.
Description of the Related Art
Printed circuit boards, also referred to as printed wire boards, are panels carrying and electrically connecting electronic components such as transistors and the like and, hence, form vital parts of electronic devices. Printed Circuit boards have a more or less complex structure depending on the specific application. In general a printed circuit board comprises a plurality of alternately applied conductive and insulating layers and the conductive layers are bonded together by hardening panels or plies of glass fibers impregnated with organic resin, said panels forming the insulating layers. Such panels for use in the production of printed circuit boards are widely known in the industry as “prepregs” (preimpregnated fibres), which are delivered and processed in an uncured, hence viscous state of the organic resin. The actual insulating layer results when the organic resin has cured. The insulating layers carry conductive layers, for example formed of copper foil, the conductive layers being appropriately processed to form wirings to electrically connect the electronic components. While insulating layers are mostly continuous to provide electric insulation between the conductive layers of the printed circuit board, the conductive layers are usually strongly patterned and open work. Modern printed circuit boards allow for a high degree of integration of electronic components and their appropriate wiring. In the technical field of printed wire boards, substrates are known to offer similar functionality in terms of alternately applied conductive and insulating layers, however, substrates are much smaller and often serve to connect a microchip to a printed circuit board. To this end, the insulating layers of substrates are often produced of glass or ceramic materials which allows for smaller, high-precision structures.
There is, however, a constant need for further miniaturization in the electronic industry in order to provide consumers and professionals with ever smaller yet more capable electronic devices and installations which require more electronic components to be packaged and wired in a smaller space. There are a number of applications that use cavities arranged in a printed circuit board, offering the possibility to arrange electronic components therein. Especially components such as microphones and loudspeakers consume considerable space on a printed circuit board and there is, thus, the need to provide such functionalities on a printed circuit board without mounting such components on the surface of a printed circuit board.